title: Nuclear localization of pyruvate dehydrogenase complex-E2 (PDC-E2), a mitochondrial enzyme, and its role in signal transducer and activator of transcription 5 (STAT5)-dependent gene transcription.
abstract: STAT (signal transducer and activator of transcription) proteins play a critical role in cellular response to a wide variety of cytokines and growth factors by regulating specific nuclear genes. STAT-dependent gene transcription can be finely tuned through the association with co-factors in the nucleus. We showed previously that STAT5 (including 5a and 5b) specifically interacts with a mitochondrial enzyme PDC-E2 (E2 subunit of pyruvate dehydrogenase complex) in both leukemic T cells and cytokine-stimulated cells. However, the functional significance of this novel association remains largely unknown. Here we report that PDC-E2 may function as a co-activator in STAT5-dependent nuclear gene expression. Subcellular fractionation analysis revealed that a substantial amount of PDC-E2 was constitutively present in the nucleus of BaF3, an interleukin-3 (IL-3)-dependent cell line. IL-3-induced tyrosine-phosphorylated STAT5 associated with nuclear PDC-E2 in co-immunoprecipitation analysis. These findings were confirmed by confocal immunofluorescence microscopy showing constant nuclear localization of PDC-E2 and its co-localization with STAT5 after IL-3 stimulation. Similar to mitochondrial PDC-E2, nuclear PDC-E2 was lipoylated and associated with PDC-E1. Overexpression of PDC-E2 in BaF3 cells augmented IL-3-induced STAT5 activity as measured by reporter assay with consensus STAT5-binding sites. Consistent with the reporter data, PDC-E2 overexpression in BaF3 cells led to elevated mRNA levels of endogenous SOCS3 (suppressor of cytokine signaling 3) gene, a known STAT5 target. We further identified two functional STAT5-binding sites in the SOCS3 gene promoter important for its IL-3-inducibility. The observation that both cis-acting elements were essential to detect the stimulatory effect by PDC-E2 strongly supports the role of PDC-E2 in up-regulating the transactivating ability of STAT5. All together, our results reveal a novel function of PDC-E2 in the nucleus. It also raises the possibility of nuclear-mitochondrial crosstalk through the interaction between STAT5 and PDC-E2.
authors.affiliation: Department of Microbiology and Immunology, H. M. Bligh Cancer Research Laboratories, Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL 60064, USA.
authors.forename: Fu-Yu
authors.initials: FY
authors.lastname: Chueh
authors.forename: King-Fu
authors.initials: KF
authors.lastname: Leong
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Cronk
authors.forename: Srividya
authors.initials: S
authors.lastname: Venkitachalam
authors.forename: Samantha
authors.initials: S
authors.lastname: Pabich
authors.forename: Chao-Lan
authors.initials: CL
authors.lastname: Yu
mesh_terms: D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology*; D051047:Dihydrolipoyllysine-Residue Acetyltransferase / Q000378:metabolism*; D017930:Genes, Reporter; D047468:Immunoprecipitation; D007377:Interleukin-3 / Q000494:pharmacology; D054878:Lipoylation; D049410:Luciferases, Renilla / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D008928:Mitochondria / Q000201:enzymology*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D050799:STAT5 Transcription Factor / Q000378:metabolism*; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D007377:Interleukin-3; D050799:STAT5 Transcription Factor; C491411:Socs3 protein, mouse; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D049410:Luciferases, Renilla; D051047:Dihydrolipoyllysine-Residue Acetyltransferase